Method and device for the production of brake linings or clutch linings made of pressing materials that are bonded by means of a bonding agent

ABSTRACT

A pressing device having a pressure stamp ( 1 ), the sides of which are surrounded by a circumferential wall ( 2 ). The circumferential wall ( 2 ) is movable counter to the direction of movement of the pressure stamp ( 2 ) during and/or after the pressing process, a gap ( 7 ) being formed between the pressing material and the circumferential wall ( 2 ). The vapors radially escape from the friction lining during and/or after the pressing process and are evacuated via the gap ( 7 ), the pressure of the pressure stamp being maintained at least at a reduced level during the entire pressing process.

The invention relates to a method of producing friction linings madefrom pressing material bonded by means of a binder, particularly brakelinings or clutch linings, wherein

the pressing material is filled into a mould or receptacle,

the pressing material is pressed with at least one ram-like pressingtool, and

gaseous or vaporous media which are contained in the mould or areproduced during the pressing operation are drawn off from the mould.

The invention further relates to apparatus for producing frictionlinings made from pressing material bonded by means of a binder,particularly brake linings or clutch linings, with

a receptacle or mould to receive the pressing material,

a ram-like pressing tool which can be moved in and out of the mould andcompresses the pressing material, and

a counter-pressure plate as an abutment for the pressing force exertedby the pressing tool.

During the processing of pressing material containing binder reactiongases are produced during the cross-linking of the binders. Since thepressing material, which is usually present in the form of bulkmaterial, is compressed, the air which is compressed with it and heatedin the press mould must be removed from the friction lining. During thecompression of the pressing material, which usually proceeds underpressure and temperature, hydrogen or other reaction gases, e.g.ammonia, can be produced due to other components. These gases must alsobe removed from the friction lining. In the past this took place betweenthe individual pressing operations, since drawing off of the gases isnecessary for the progress of binder reactions and for the production ofa homogeneous friction lining. In the past the procedure was such thatthe pressing tool, i.e. the press ram, is opened against the pressingmovement and closed again after the degassing of the friction lining.When pressure and heat are applied again further gases may be produced,and these must likewise be drawn off. The degassing stroke of the pressram is repeated. This is time-consuming. Long overall pressing times arethe result. Moreover, the reactions in the pressing material can onlyproceed at intervals during compression of the pressing material to formthe friction lining. In some circumstances this leads to incompletecuring of the friction lining and to inhomogeneities in the frictionlining.

The known type of degassing has a further disadvantage. Due to the hotsmooth surface of the press ram the surface of the friction lining isoften so smooth as to be “glassy” and thus has poor permeability for gasdiffusion. However, the gases must diffuse out of the friction liningagainst the pressing direction—that is to say over the smooth surface.As has been stated, this is not readily possible. Because of the lowinherent strength of the friction lining at the time of degassing, theinternal gas pressure can lead to cracks, bubbles and delaminations. Afriction lining with such defects is unusable.

In order to avoid the described disadvantages, a method of producingbrake linings has been developed (DE 199 53 438 A1) in which degassingof the friction lining takes place continuously during the pressingstroke. The degassing of the friction lining takes place during thepressing operation via bores constructed in the press ram. In this waythe mass production of brake linings has been improved, particularlywith regard to the pressing time, by comparison with degassing byopening the pressing tool. However, inhomogeneities leading to rejectionof friction linings can still occur.

The object of the invention is to improve the quality of the frictionlinings produced whilst maintaining the shortest possible pressingtimes.

In order to achieve this object, the method referred to in theintroduction is characterised in that the gaseous or vaporous media tobe drawn off are drawn off during and/or after the pressing operationradially or/and via the side of the friction lining facing away from thepressing tool, the pressure exerted by the pressing tool on the frictionlining being maintained at least at a reduced level.

The invention combines several advantages. On the one hand the pressingtimes can be kept to a minimum. There is no need for venting cycles,that is to say no moving of the pressing tool into and out of the mould.On the contrary, degassing can take place continuously. Due to theaction of the pressing tool (that is to say by supply of pressure andheat) during the entire pressing operation the friction lining can curehomogeneously. In particular, the reactions taking place at an elevatedtemperature proceed completely and within the shortest possible time.The curing process is favoured by the fact that the surfaces of thelining are constantly in contact with the heated tool. Thus separatecuring can be omitted.

A further advantage lies in the high quality of the friction liningsproduced. Because the pressure is maintained at least at a reducedlevel, the internal gas pressure cannot destroy the lining—unlike in theprior art. There are considerably fewer rejects. Furthermore, thecompressibility of the friction lining can be set specifically byadjustment of the clamping force and/or the clamping path.

The friction lining can emit gas via its entire radial area. Theinvention is based on the recognition that in a direction at rightangles to the pressing direction the friction lining has the lowestdiffusion resistance for the enclosed gases due to the structuregenerated in the pressing material during pressing. Cracks, bubbles,delaminations, etc., in the surface regions of the friction lining aremarkedly reduced.

As an alternative or in addition to this, it is possible to draw off thegaseous or vaporous media during and/or after the pressing operation viathe side of the friction lining facing away from the pressing tool. Theside of the friction line facing away from the pressing tool cures“last” and allows complete degassing of the friction lining. Also as aresult any damage is effectively prevented particularly to the surfaceregions of the side of the friction lining facing the pressing tool.

In a preferred further development of the invention it is proposed thatat least during a phase of the pressing operation between the frictionlining and an appertaining complementary lateral wall of the mould a gapis produced into which the gaseous or vaporous media enclosed in thepressing material diffuse out and are then drawn off. Already after ashort shaping phase of the friction lining, the side wall thereof canalso be completely exposed radially, as is preferably proposed. Thepressure and optionally the introduction of heat via the end face of thefriction lining are maintained at least at a reduced level.

The invention is suitable for friction linings of all types. However, itis directed in particular to brake linings or clutch linings. Brakelinings for drum brakes can be produced according to the invention injust the same way as disc brake linings. In a preferred embodiment ofthe invention, therefore, it is proposed that preferably after thepressing material has been filled into the mould the latter is providedwith a support plate and the gaseous or vaporous media are drawn off outof the mould radially and/or via openings constructed in the supportplate. During the compression of the pressing material the frictionmaterial is joined to the support plate, either by an adhesive layer orby the adhesive properties of the pressing material.

The support plate is preferably supplied with pressure by way of acounter-pressure plate acting against the pressing tool, and the gaseousor vaporous media are drawn off between the support plate and thecounter-pressure plate towards the surrounding atmosphere. For thispurpose a channel can be provided in the counter-pressure plate or inthe support plate (or in both). The channel creates a connection betweenthe openings in the support plate and the surrounding atmosphere. Sincethe channel or channels only occupy a very small surface area incontrast to the overall effective surface, they are entirely uncriticalboth for the contact region and also for the support plate.

As an alternative or in addition, the gaseous or vaporous media can alsobe drawn off to the atmosphere through the counter-pressure plate. Inthe production of a friction lining with a support plate the openings inthe counter-pressure plate are preferably aligned with the openingsconstructed in the support plate.

In order to achieve the object the apparatus according to the inventionwhich is referred to in the introduction is characterised in that aradial peripheral wall is provided for lateral shaping of the frictionlining and can be displaced relative to the press ram and to thecounter-pressure plate or vice versa. After a short shaping phase of thefriction lining the peripheral wall can be “lowered”, so that the sidesof the friction lining are then exposed for degassing. A gap is producedinto which gases or vapours diffuse out. The gap can be enlarged to suchan extent that the side surfaces of the friction lining are completelyexposed. Naturally it is possible—although more complex—to keep theperipheral wall stationary and to move the press ram together with thecounter-pressure plate relative to the peripheral wall.

The object is also achieved by an apparatus as referred to in theintroduction in which at least one opening which creates a connectionbetween at least a part-zone of the friction lining surface and thesurrounding atmosphere is associated with the side of the frictionlining facing the counter-pressure plate. As already mentionedpreviously, it may advantageously be provided that channel-likedepressions which connect at least a part-zone of the friction lininglaterally to the surrounding atmosphere are constructed in the side ofthe counter-pressure plate facing the friction lining. The channel-likedepression can be constructed for example as grooves through which thefriction lining is degassed.

In order to produce a disc brake lining it is proposed that between thecounter-pressure plate and the pressing material there is disposed asupport plate which is supported on one side against thecounter-pressure plate and is supplied from the other side with thepressing material, the support plate and the pressing material formingthe friction lining.

The friction lining can be degassed radially in the described manner.For alternative or additional degassing the support plate has at leastone support plate opening through which the gaseous or vaporous mediaare drawn off.

The support plate openings advantageously have a shape which widensoutwards like a funnel and can be produced during a simple punchingoperation. The counter-pressure plate can be provided with projectionswhich preferably engage partially in the support plate openings, leavinga residual gap through which the gases can escape.

Finally, in a significant further development of the invention it isproposed that the counter-pressure plate has at least one throughopening which connects at least a part-zone of the friction lining tothe surrounding atmosphere. Thus the gases are led through thecounter-pressure plate to the surrounding atmosphere. The throughopenings are advantageously aligned with the support plate openings.

An insert, a so-called stopper ram, can be inserted into the throughopening in the counter-pressure plate. An annular gap remains betweenthe stopper ram and the through opening. The counter-pressure plate isprovided on its side facing away from the friction lining with a groovewhich leads the gases from the annular gap outwards. The annular gap isset so that no pressing material or friction material can escape intothe gap between the stopper ram and the counter-pressure plate.

The area at which the gases escape can be wear. Therefore when thestopper ram shows signs of wear it is simply removed and replaced by anew stopper ram.

The invention is explained in greater detail in the followingdescription with reference to a preferred embodiment in conjunction withthe appended drawings, in which:

FIGS. 1 and 2 shows a schematic sectional view through a firstembodiment of an apparatus according to the invention in the completelyclosed press end position and a subsequent degassing position in whichthe gases included in the friction lining can diffuse out radially;

FIG. 3 shows a second embodiment of a pressing apparatus according tothe invention in which the gases and/or vapours are drawn off throughthe counter-pressure plate;

FIG. 4 shows a third embodiment which is modified relative to theembodiment according to FIG. 3 and in which the gases or vapours aredrawn off from the friction lining via channels in the rear face of thesupport plate;

FIG. 5 shows a schematic perspective sectional view through a fourthembodiment in which the gases or vapours are drawn off through thecounter-pressure plate; and

FIG. 6 shows a side view of a stopper ram as inserted into thecounter-pressure plate in FIG. 5, but on an enlarged scale.

A pressing apparatus for producing brake linings for disc brakes ofmotor vehicles is shown in FIG. 1. The pressing apparatus has a pressram 1 which is movable relative to a peripheral wall 2. The peripheralwall is kept stationary. It forms together with the ram 1 a receptacleor mould for pressing material 3 which is present in the initial stateas bulk material and which forms the friction lining after compressionby the press ram.

A support plate 4 made from metal rests on the peripheral wall 2. Duringthe compression of the pressing material 3 the pressing material isapplied so as to adhere firmly to the support plate 4. Thecounter-pressure of the ram 1 during compression is applied by way of acounter-pressure plate 5.

In detail, a brake lining is produced as follows: first of all the ram 1is in a lowered position. The mould formed by the press ram 1 and theperipheral wall 2 is open at the top. A defined quantity of pressingmaterial 3 is filled into the mould. Then the support plate 4 is placedon the peripheral wall 2 and pretensioned by the counter-pressure plate5. The press ram 1 then compresses the pressing material against thesupport plate 4. In this case the pressing material can already becompressed to for example ⅕ of its volume.

Openings 6 are constructed in the support plate 4 into which thepressing material can penetrate at least slightly during compression andthus creates an additional mechanical anchoring. As a rule the openings6 are punched and therefore are of slightly conical construction. Theopenings 6 are not obligatory. They do form a positive-lockingconnection between the friction lining and the support plate 4 (an inparticular a high resistance to shear forces), although thepositive-locking connection between the friction lining and the supportplate is quite sufficient for a reliable connection.

The press ram 1 is heated during the pressing operation. During thepressing operation the pressing material 3 is pressed into the mould andcured with additional heat energy being supplied. In this case gases orvapours are produced which must be drawn off from the mould in order notto lead to damage to the friction lining and thus to rejection thereof.

FIG. 2 shows how according to the invention the peripheral wall 2 isopened in the downward direction for degassing. This can already takeplace after a short shaping phase of the friction lining in which thefriction lining acquires sufficient stability to retain its shape evenwithout the peripheral wall 2. When the peripheral wall 2 is lowered agap 7 is formed. The gaseous or vaporous media can diffuse out into thegap 7 and are drawn out of the mould. In FIG. 2 the mould is shown onlypartially open. Naturally, and preferably, the entire side wall of thefriction lining can also be exposed either by lowering of the peripheralwall, as illustrated, or by simultaneous raising of the press ram 1together with the counter-pressure plate 5 and the brake lining heldbetween them.

During the entire venting, the pressure of the press ram 1 is maintainedat least at a reduced level. Also the introduction of heat can takeplace continuously. The result is a homogeneous brake lining ofexcellent quality which can be produced in the shortest possible time.

If for any reason the pressing material 3 should not be completelysolidified—that is to say stable in shape—then after the peripheral wall2 has been lowered it can also be raised again to close the mould inorder to stabilise the radial shape of the lining.

When the friction lining is completely solidified and the unwantedgaseous components have diffused out, the finished brake lining can beremoved from the mould.

The embodiment of the apparatus shown in FIG. 3 corresponds to the basicconstruction of the press mould shown in FIGS. 1 and 2, so that in orderto avoid unnecessary repetitions only the modifications which have beenmade will be described, whilst for other matters reference may be madeto the preceding description of FIGS. 1 and 2. The components whichcorrespond in functional terms are given the same reference numerals inthe drawings.

In the embodiment according to FIG. 3 the degassing the resultingfriction lining should take place continuously during the pressingoperation via the through openings 6 in the support plate 4. In order toachieve this channel-like depressions 8 are produced in the pressuresurface of the counter-pressure plate 5 abutting the support plate 4.The said depressions are led from the zone of the counter-pressure plate5 lying close to the through openings 6 to the outer atmosphere.

In each of its zones lying opposite the through openings 6 of thesupport plate the counter-pressure plate 5 has a projection in the shapeof a truncated cone which engages in the through opening 6 during thepressing operation. The projections have a smaller cross-section thatthe through openings 6, so that they do not completely close the throughopenings 6. The gases and vapours can diffuse out in this way. It shouldbe pointed out that a projection is not absolutely necessary. Asubstantially planar surface over the through openings 6 is likewisepreferred.

FIG. 4 shows an embodiment in which channel-like depressions 8′ are madein the flat face of the support plate 4 facing the counter-pressureplate 5. Otherwise this embodiment corresponds completely to thepreviously described embodiment, that is to say the gaseous or vaporousinclusions in the pressing material are drawn off continuously duringthe pressing operation via the through openings 6 and the channel-likedepressions 8′ which extend from the through openings 6 to the edge ofthe respective support plate 4.

FIG. 5 illustrates a further possibility for drawing off gaseous orvaporous media. The press mould is shown closed.

A stopper ram 9 which is substantially aligned with the through opening6 in the support plate 4 is inserted into the pressure plate 5. Thestopper ram 9 forms together with the counter-pressure plate 5 on itsunderside a substantially planar plane, wherein a first annular space 10remains between the stopper ram and the counter-pressure plate. Mediawhich are diffusing out can enter this annular space, and are led offthrough longitudinal grooves 11 constructed in the stopper ram 9 into asecond annular space 12 and from there into a lateral discharge channel13 to the surrounding atmosphere.

The second annular space 12 is necessary in particular when a componentof the pressing apparatus which rests flat on the counter-pressure platein the region of the stopper ram 9 acts on the counter-pressure plate 5.The gases are drawn off through the annular space 12 and the channel 13“below” the upper face of the counter-pressure plate 5.

The stopper ram 9 is subject to some wear. Moreover, it can be used inorder by means of impressions formed on its underside to identify thebrake lining by stamping friction material coming into the support plateopening 6. Such an identification can for example include the type offriction material or it may meet other customer-specific requirements.

In FIG. 6 the stopper ram 9 is shown by itself on an enlarged scale. Theillustrated stopper ram 9 has four grooves 11. Naturally, one groove 11is already sufficient, but care should be taken that pressing material 3can enter into the first annular space 10 between the stopper ram 9 andthe counter-pressure plate 5 and may close off the sole groove 11.Therefore a plurality of grooves 11 are advisable for more reliable andmore uniform drawing off the gases. The stopper ram 9 has on its upperface a peripheral step 14 with which it rests on a should 15 of thecounter-pressure plate 5 (FIG. 5). On its lower face the stopper ram 9has a projection 16 in which for example an impression can be made foridentification of the brake lining.

Modifications are of course possible within the scope of the invention.Thus radial venting of the brake lining can take place not only bylowering of the peripheral wall 2 but also—as already mentioned—by“moving out” the brake lining gripped between the press ram 1 and thecounter-pressure plate 5. Also the pressing apparatus is not fixed inthe orientation illustrated in the drawings. Filling of the pressingmaterial 3 from above onto a counter-pressure plate 5 or support plate 5already resting on the peripheral wall 2 is also conceivable. Finally,it should be explicitly pointed out again that the invention has beendescribed in connection with a brake lining with a support plate 4, butthe support plate 4 does not necessarily have to be a component of thebrake lining. Accordingly the invention can also be applied for exampleto the production of drum brake linings (which have no support plate).

1-16. (canceled)
 17. A Method of producing friction linings made frompressing material bonded by means of a binder, comprising the steps of:filling the pressing material into a mould, pressing the pressingmaterial with at least one ram-like pressing tool, and drawing offgaseous or vaporous media which are contained in the mould or areproduced during the pressing operation from the mould, while thepressure exerted by the pressing tool on the friction lining ismaintained at least at a reduced level, wherein the gaseous or vaporousmedia to be drawn off diffuse out and are then drawn off through a gapwhich is produced at least at times during the pressing operationbetween the friction lining and an appertaining complementary lateralwall of the mould.
 18. The Method of claim 17, wherein the gaseous orvaporous media to be drawn off are drawn off during the pressingoperation via the side of the friction lining facing away from thepressing tool.
 19. The Method of claim 18, wherein after the pressingmaterial has been filled into the mould the latter is provided with asupport plate, and the gaseous or vaporous media are drawn off out ofthe mould via openings constructed in the support plate
 20. The Methodof claim 19, wherein the support plate is supplied with pressure by wayof a counter-pressure plate acting against the pressing tool, and thegaseous or vaporous media are drawn off between the support plate andthe counter-pressure plate towards the surrounding atmosphere.
 21. TheMethod of claim 19, wherein the support plate is supplied with pressureby way of a counter-pressure plate acting against the pressing tool, andthe gaseous or vaporous media are drawn off to the atmosphere throughthe counter-pressure plate.
 22. An Apparatus for producing frictionlinings made from pressing material bonded by means of a bindercomprising: a mould to receive the pressing material, a ram-likepressing tool which can be moved in and out of the mould and compressesthe pressing material, a counter-pressure plate as an abutment for thepressing force exerted by the pressing tool, and a radial peripheralwall for lateral shaping of the friction lining, wherein saidradial-peripheral wall can be displaced relative to the press ram and tothe counter-pressure plate or vice versa during the pressing operation,so that a lateral gap is produced.
 23. The Apparatus of claim 22,wherein channel-like depressions which connect at east a part-zone ofthe friction lining laterally to the surrounding atmosphere areconstructed in the side of the counter-pressure plate facing thefriction lining.
 24. The Apparatus of claim 22, wherein during thecompression between the counter-pressure plate and the pressing materialthere is disposed a support plate which is supported on one side againstthe counter-pressure plate and is supplied from the other side with thepressing material, the support plate and the pressing material beingconnected to form the friction lining.
 25. The Apparatus of claim 24,wherein at least one support plate opening for drawing off the gaseousor vaporous media is constructed in the support plate between thecounter-pressure plate and the pressing material.
 26. The Apparatus ofclaim 22, wherein the counter-pressure plate has at least one throughopening which connects at least a part-zone of the friction lining tothe surrounding atmosphere.
 27. The Apparatus of claim 26, wherein thethrough opening is formed between a removable insert received in thecounter-pressure plate and the counterpressure plate.
 28. An Apparatusfor producing friction linings made from pressing material bonded bymeans of a binder, comprising: a mould to receive the pressing material,a ram-like pressing tool which can be moved in and out of the mould andcompresses the pressing material, a counter-pressure plate as anabutment for the pressing force exerted by the pressing tool, and atleast one opening creating a connection between at least a part-zone ofthe friction lining surface and the surrounding atmosphere and beingassociated with the side of the friction lining facing thecounter-pressure plate.
 29. The Apparatus of claim 28, whereinchannel-like depressions which connect at least a part-zone of thefriction lining laterally to the surrounding atmosphere are constructedin the side of the counter-pressure plate facing the friction lining.30. The Apparatus of claim 28 wherein during the compression between thecounter-pressure plate and the pressing material there is disposed asupport plate which is supported on one side against thecounter-pressure plate and is supplied from the other side with thepressing material, the support plate and the pressing material beingconnected to form the friction lining.
 31. The Apparatus of claim 30,wherein at least one support plate opening for drawing off the gaseousor vaporous media is constructed in the support plate between thecounter-pressure plate and the pressing material.
 32. The apparatus ofclaim 28, wherein the counter-pressure plate has at least one throughopening which connects at least a part-zone of the friction lining tothe surrounding atmosphere.
 33. The Apparatus of claim 32, wherein thethrough opening is formed between a removable insert which is receivedin the counter-pressure plate and the counter-pressure plate.
 34. AMethod of producing friction linings made from pressing material bondedby means of a binder, comprising: filling the pressing material into amould, pressing the pressing material with at least one ram-likepressing tool, and drawing off gaseous or vaporous media which arecontained in the mould or are produced during the pressing operationfrom the mould, while the pressure exerted by the pressing tool on thefriction lining is maintained at least at a reduced level, wherein thegaseous or vaporous media to be drawn off are drawn off during thepressing operation via the side of the friction lining facing away fromthe pressing tool.
 35. The Method of claim 34, wherein after thepressing material has been filled into the mould the latter is providedwith a support plate, and the gaseous or vaporous media are drawn offout of the mould via openings constructed in the support plate.
 36. TheMethod of claim 35, wherein the support plate is supplied with pressureby way of a counter-pressure plate acting against the pressing tool, andthe gaseous or vaporous media are drawn off between the support plateand the counter-pressure plate towards the surrounding atmosphere. 37.The Method of claim 35, wherein the support plate is supplied withpressure by way of a counter-pressure plate acting against the pressingtool, and the gaseous or vaporous media are drawn off to the atmospherethrough the counter-pressure plate.